When using a portable hand-held circular power saw to make a linear or straight cut in an object, such a piece of timber, the user attempts to push the power saw forwards by hand, along a linear path, to make the straight cut.
A problem with such portable, hand-held saws is that, as the saw is pushed forwards when making the cut, the user can find it difficult to manually control the saw precisely along the linear path. In other words, the cut, which ought to be perfectly straight, can end up being crooked. This deficiency is inherent in portable hand-held power saws because, as the rotating saw blade cuts through the timber, it exerts forces that tend to cause the saw to deviate from or veer off the intended linear path.
Problem: Clamping Leads to Loss of Time-Efficiency
To address the above problem of the saw veering away from the linear path, the prior art includes known saw guides that have a linear guide intended to help the user make straight cuts with a hand-held, portable, power saw.
Prior art examples of such saw guides are seen in U.S. Pat. No. 6,752,059 (Posont), U.S. Pat. No. 6,708,422 (Stojanovski) and U.S. Pat. No. 3,645,307 (Stocker).
A problem which is common to each of these prior art, however, is that each of these saw guides is designed to be clamped in place by some clamping implement. Typically, the saw guide is clamped or fastened motionless to the object which is to be cut.
The length of time needed for this clamping process can be, for example, anywhere from 30 seconds to perhaps more than a minute or so. This may not seem an excessive amount of time, but it must be remembered that professional carpenters often need to male around 300 or more of such angle-cuts per day. Thus, the extra 30-60 seconds or more per cut, needed to clamp the saw guide for each cut, when multiplied by 300 per day, would add about two to five extra hours per day.
Problem: Limitation of Range of Movement of the Saw
In prior art FIG. 1A, the saw 20 is shown at the beginning of its run, before it is pushed forward alongside the guide 10 with the intention of making a straight cut in an object 1. Often, the linear cut must be created at an angle to an external surface of the object (“angle cut”). For instance, a carpenter may need to make a cut which is at forty-five degrees with respect to an edge of the timber 1.
In prior art FIGS. 1B and 1C, in order to make an angle cut, the linear guide 10 is pivotally connected to an anchoring device 30. The anchoring device 30 is fastened motionless to the object 1 by a mandatory locking device 32. (Details of the locking device 32 are not shown in the drawings, and are merely drawn as a rectangle in the drawings, since, in the prior art, there is a range of suitable locking mechanisms). After the anchoring device 30 is locked to the object 1, the guide 10 is then oriented at a selected angle, and fastened to the anchoring device 30 at that angle. The user then pushes the portable power saw 20 against and alongside the linear guide 10 to create the angle cut in the object 1.
FIG. 1A shows the linear guide 10 perpendicular to the object 1, while FIGS. 1B and 1C show the same linear guide 10 arranged at other selected angles.
The point 40, where the linear guide 10 pivots about the anchoring device 30, is called the pivotal axis or the pivot point 40. For instance, in prior art FIGS. 1A, 1B and 1C, the pivot point 40 is found an intersection 450 of the linear guide 10 and the anchoring device 30. Specifically, the pivotal axis 40 passes through some part of the linear guide 10. In other words, there is no separation or distance between the linear guide 10 and the pivot point or pivotal axis 40, and this causes a problem in the prior art.
To explain the problem, by way of background, it is noted that in FIGS. 1A, 1B and 1C, the line of cut 21 is parallel to, but distanced from the linear guide 10, shown as the distance x in FIG. 1A. As mentioned above, this is because saw blades 13 in right-hand, portable power saws usually lie in a plane that is located proximate the right-hand side of the saw's housing. (The drawing assumes the saw 20 is a more common right-hand saw for right-handed users, rather than the rarer left-hand saw).
The problem, which stems from the lack of separation of the guide 10 and the axis 40, may not be apparent from FIGS. 1A and 1B, because there the saw 20 is able to move sufficiently back along the guide 10 for the saw blade to be clear of the object 1. (In FIGS. 1A, 1B and 1C, the edge of the saw blade 13 is located proximate an area identified by numeral 20A). In FIGS. 1A and 1B, prior to the saw 20 commencing the cut, the location 20A of the blade of the saw faces the object 1. (The words “faces” or “facing” in this context refer to the saw before it is pushed to commence its cut, as the saw “faces” the object in, for instance, FIGS. 1A, 2A and 3A).
The problem, however, is more evident in the arrangement in FIG. 1C where the guide 10 is arranged at an acute angle with respect to the object 1, with the saw 20 positioned at the beginning of the guide 10, where it would be located before it begins its cutting motion along the guide.
The problem in FIG. 1C is that the saw 20 is too close to the object 1, even when the saw 20 is pulled as far back along the guide 10 as possible. (The problem pertains to the part of FIG. 1C around reference numeral 25). In FIG. 1C, even if the saw 20 were to be drawn as far back as possible along the guide 10, the location 20A of the blade is positioned over and above the object 1 itself, rather than facing the object as in FIGS. 1A and 1B.
A circular saw cannot commence a cut when positioned over and above the object 1, which is the problem of FIG. 1C. Ideally, before the cutting commences, there must be a space between the circular blade 13 of the saw 20 and the object 1, so that the commencement of sawing involves pushing the rotating blade into the object 1. This is impossible in FIG. 1C, because the saw 20 cannot be drawn back far enough, while maintaining sufficient stability from the guide 10.
An imperfect solution to the problem of FIG. 1C is to extend the length of guide 10 backwards, to enable the saw 20 to be placed further away from the object, as shown in FIG. 1CC. This enables the location 20A of the leading edge of the saw blade to be face the object 1 before commencement of cutting. While this partially solves the problem, it is, however, an imperfect solution, because it would result in a longer starting-end for the guide 10.
(Compare FIG. 1C with FIG. 1CC, with the latter drawing showing the longer guide 10). In FIG. 1CC, if the saw 20, which is relatively heavy, is positioned a greater distance from the support of the anchoring device 30, it would potentially lead to a more unstable cantilever 10A. Having the saw 20 perched at the end of a long, unstable cantilever 10A, is not an ideal position for the user to commence pushing a power saw along the guide.
The problem in FIG. 1C is found in a number of prior art saw guides, such as U.S. Pat. No. 3,645,307 (Stocker). In FIG. 1 of Stocker, the pivotal axis of the base frame 11, relative to the guide rail 40, is located at an intersection of two components. The pivotal axis is shown by numeral 54 in FIG. 1 of Stocker. In Stocker's saw guide, there is no separation of the guide and the pivotal axis. Thus, Stocker is susceptible to the problem of FIG. 1C of the present specification, because of the problematic location of the pivotal axis in Stocker.
Another example of this problem is in the abovementioned U.S. Pat. No. 6,708,422 (Stojanovski). In FIGS. 2 and 9 of Stojanovski, the pivot point or pivotal axis passes through part of the linear saw guide. In other words, there is no separation of the pivotal axis or pivot point from the linear saw guide.
In this regard, in Stojanovski's drawings, the bolt 248 passes through main pivot holes 152, 170, and through a small semi-circular cutaway in the arm assembly 38. Thus, the Stojanovski patent is also susceptible to the problem in FIG. 1C of the present specification, if the saw 20 were to be pushed in a direction that urges the anchoring device 30 towards the object 1.
Stojanovski avoids the problem of the present FIG. 1C by have the saw come from the other direction, but in so doing creates another problem.
To explain this, FIG. 1D illustrates a simplified representation of Stojanovski. In FIG. 1D, the force with which the user pushes the saw 20 will, particularly at certain angles, include a force component 23 that has the effect of urging the anchoring device 30 away from the object 1. Therefore, to operate the Stojanovski saw guide, it is mandatory that its anchoring means must be locked or clamped to the object by some form of locking mechanism 32. For instance, in FIG. 1 of Stojanovski, the saw guide cannot function if the fixed arm assembly 35 is not locked or clamped to the object.
In Stojanovski, for each cut, the step of un-clamping and re-clamping the fixed arm assembly to the object may take only perhaps 30 to 60 seconds. But it must be remembered that professional carpenters often need to make around 300 or more angle-cuts per day. An extra 30-60 seconds per cut, multiplied by 300 per day, would add about two to five extra hours per day. Therefore, the mandatory locking or clamping device in Stojanovski, and also in Stocker mentioned above, and in other known prior art saw guides, wastes a significant amount of time when used in high volume situations faced by professional carpenters, builders and other such tradesmen.
Another problem in Stojanovski, and other known prior art saw guides, is that the portable power saw is not attached to the linear guide (the variable angle arm assembly 38 of Stojanovski's FIG. 1). Hence, when making a cut, the user, as well as pushing the saw forwards, must also push the saw sideways to maintain the saw against the linear guide. (In prior art FIGS. 1A, 1B, 1C, 1CC and 1D of the present drawings, this sideways force, exerted by the user to keep the saw against the saw guide, is represented as arrow 22).
Firstly, this sideways force 22 is another reason why a clamping or locking device is mandatory in Stojanovski. In the present FIG. 1D, without such clamping, the sideways force 22, and its force components 23, would push the anchor device 30 out of alignment.
Secondly, in practice, the sideways force 22 exerted by the user may be adequate to maintain the saw 20 against the guide 10, and insufficient to ensure a perfectly straight cut. This is because rotating circular saws, in hand-held power saws, can often bite into the material and exert forces which cause the circular saw to veer off course, particularly if the user's sideways force 22 is insufficient.
In the prior art, the problem of simple saw guides, which are not connected to the saws, is exacerbated in the case of variable-angle saw guides. Since the guides 10 can be oriented at many different angles, there is likewise a great variation in the direction of the sideways forces 22 needed to keep the saw 20 abutted against the guides 10. Therefore, in the prior art, the use of locking or clamping mechanism in these prior art variable-angle guides is mandatory. For instance, both Stocker and Stojanovski require such mandatory locking or clamping mechanisms. And, as mentioned, the short time needed to clamp the anchoring device to the object can waste literally several hours each day for a professional carpenter needing to make several hundred angle-cuts per day.
An object of the present invention is to overcome or at least ameliorate one, or preferably more than one, of the abovementioned problems in the prior art of portable cutting guides, or to provide an improved alternative.
Description and discussion of prior art in this specification should not be taken as an admission that any one, or any combination of the prior art, is part of the common general knowledge of the skilled addressee.